Method and means for tensioning and for mounting diaphragms



June 14, 1932. SMYTHE 1,863,073

METHOD AND MEANS FOR TENSIONING AND FOR MOUNTING DIA'PHRAGMS Filed April23. 1930 2 Sheets-Sheet l INVENTOR E. H. SMYrHE 6 28 9mm 6, M

A T TO/PNE Y June 14, H HE METHOD AND MEANS FOR TENSIONING AND FORMOUNTING DIAPHRAGMS Filed April '25. 1930 2 Sheets-Sheet 2 IIIIIIHlllllHllJ [HI I H I HI I]! lNl/ENTOR 5. H SMVTHE V WMKM A TTOR/VEVPatented June 14, 1932 UNITED STATES PATENT orrlca EDWIN H. SMYTHE, FEVANSTON, TLLINOIS, ASSIGNOR T0 BELL TELEPHONE LABO- RATORIES,INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK METHOD ANDMEANS FOR TENSION ING AND FOR MOUNTING DIAPHRAGMS Application filedApril 28,

This invention relatesto a method of and means for uniformly stretchingmetal diaphragms or membranes to be used in acoustic devices in generaland more particularly in phonographs, transmitters, receivers, loudspeakers and the like.

The object of this invention is to uniformly tension metallic diaphragmsto any desired degree in a simple, cheap, accurate and time saving waywhich requires a minimum of skill or knowledge on the part of theoperator.

The feature of this invention consists in heating the diaphragm bypassing an electric current therethrough, thereby causing it to expand,the amount of expansion thereof depending upon the temperature to whichthe diaphragm material is heated. When it has reached a predeterminedtemperature, cold mounting members are clamped upon and secured to it.

Another feature of this invention consists in the provision of means inthe electric circuit of which the diaphragm material is a part toindicate to the operator that it has been heated to the predeterminedtemperature. The operator then clamps the mounting members to thediaphragm and the electric circuit is simultaneously broken whereby thediaphragm may cool and be tensioned inasmuch as it is constrained by themounting members from returning to its original condition.

Still another feature of this invention resides in the means employed incarrying out the method forming a feature of this invention.

In accordance with this invention, a strip of diaphragm material isinserted in an electric circuit which includes a source of current, acircuit resistance varying means, a switch and a current indicatingmeans. The diaphragm material is then placed between the fixed andmovable elements of a clamping device in which the mounting members towhich the diaphragm is to be secured have already been positioned one onthe movable element and one on the fixed element. An electric current isthen permitted to flow through the diaphragm material heating it andcausing it to 1930. Serial No. 44 ,691.

expand. When heated to a predetermined temperature, the current flow isinterrupted and simultaneously the movable element of the clampingdevice is brought down against the fixed element positioning themounting members on opposite surfaces of the diaphragm material to holdthem together and to prevent the contraction of the diaphragm materialto its original condition, while the mounting members are being rigidlysecured together. The means for connecting the diaphragm material in theelectric circuit are removed, the diaphragm unit is removed from theclamping device, the portion outside the mounting members trimmed off;and the diaphragm unit is ready for use.

A more complete understanding of this invention will be obtained byreference to the appended drawings wherein:

Fig. 1 is an elevational view, partly in section, of means foreffectuating the method comprising a feature of this invention;

Fig. 2 is a view of Fig. 1 along the lines 22 and shows more in detailthe nature of the movable element of the clamping device by means ofwhich the expanded diaphragm material is secured by the mountingmembers;

Fig. 3 is an enlarged section of a portion of the mounting members shownin Fig. 1 and illustrates how the lower mounting ring may beelectrically insulated from the diaphragm material;

Fig. 4 illustrates a force. producing arrangement which may be employedwith the movable element of the clamping device of Fig. 5 is a sectionto a reduced scale-of a diaphragm unit, the diaphragm unit of which hasbeen tensioned in accordance with the method forming one feature of thisinvention and assembled in the means forming another feature of thisinvention and Figure 6 is an elevational view of Fig. 1 along the line66.-

Referring now to the drawings, there is shown a rigid block 6 having anannular shoulder portion 5. A mounting member 4 in the form of a ring ofa light weight, high strength material, such as aluminium,-reststhereon, there being a slight clearance only between its inner surfaceand the annular surface 29 of the block 6. The ring 4 is provided withan annular groove 24 and with tapped drillings 26 at spaced intervalsabout its periphery. The surface of the member 4 is given a thin coating3 of an electrically insulating substance, for instance, shellac, toinsure that surface against short circuit of electric currents. Theblock 6 is provided with a layer of heat insulating material 28 such asasbestos, the upper surface of said layer being preferably in the planeof the upper surface of the mounting member 4.

Extending vertically from the rearwardl projecting portion 35 of theblock 6 is a stan ard 17 having bifurcations 30 between which a leverarm 15 is rotatably supported on the pin 31. Another lever 16 isattached at one end to arm 15 by means of a pin 32, joining itsbifurcated portions 34 and passing through and slidably movable in theslot 33 of arm 15. At its lower extremity, lever 16 passes through thecentering arm 27, which projects horizontally outward from the standard17, and fits into a cylindrical depression in member 14. It is securedtherein by a pin 20 passing through it and said member.

The member 14 includes a fiat plate portion 19 having a multiplicity ofspaced projecting portions 18, said portions defining recesses 38 whichprovide passageways for easy access to the mounting member 2 for theinsertion of fastening bolts. The portions 18, also, distribute theforce exerted on the member 14 to the mounting member 2. Supported onthe underside of these fingers is a mounting member 2 which may be ofthe same material as member 4 and likewise ring shaped. It is providedwith an annular ridge 25 which is adapted to fit into the oove 24 in themember 4. In alignment with the tapped drillings 26 in member 4 aredrillings 21. The member 2 is held in place on the movable element ofthe clamping device by a plurality of spaced depressible buttons 23acted upon at their bases by springs 22 and mounted in said member 19.

A strip of metallic diaphragm material is shown between the elements ofthe clamping device and rests upon the fiat surface formed by the ring 4and the heat insulating or thermally non-conductive material 28. On theupper surface of the diaphragm material rests a flat plate 13 of heatinsulating material, for instance, of asbestos, which acts not only toprevent heat loss when the diaphragm material is being raised to itspredetermined temperature but also to prevent heat loss after tlr'eclosed electrical circuit has been opened. This plate acts, also, tomaintain the diaphragm material in the same plane when current ispassing through it and when it is expanding. There should be suiticientclearance between the upper surface of this plate 13 and the undersurface 36 of portion 19 of member 14 to permit the mounting members tobe brought together without the plate exerting any pressure on thediaphragm material within the mounting members other than that due toits own weight. The diaphragm material 1 is shown connected to anelectric circuit, to form an element thereof, by means of elongatedclips 7 clasping the opposite edges of the diaphragm material betweentheir jaws. The remaining portion of the circuit comprises a source 9 ofelectric current, a variable resistance element 10, a switch 11 (shownin its open position) and a current indicating means 12. These elementsare connected to one another and to the clips 7 by the wires 8.

The diaphragm material is to form an element in an electric currentcarrying circuit and by the passage'of current therethrough will beheated to a desired degree to cause it to expand. The coefiicient ofexpansion of the material being known, the temperature to which thediaphragm material must be raised to obtain the desired expansion may beeasily calculated. The expansion of the diaphragm material will be ameasure of its contraction upon cooling and if it is to be constrainedagainst such contraction a measure of the tension which will be inducedin the diaphragm material by its inability to return to its originalcondition.

Hence, to

obtain a desired degree of uniform tension in the diaphragm, the extent.to which it is to be expanded and the temperature to which it must beraised must be predetermined. Furthermore, the specific resistance ofthe diaphragm material being known, or easily determinable, itsresistance at the hot temperature of the diaphragm material ismathematically ascertainable and for a given impressed voltage thecurrent flowing through said diaphragm material at that temperature maybe determined. When a closed electric circuit exists, an indicatinginstrument therein will reveal the variation in current with theincrease in temperature and when the current reading indicates that thediaphragm has reached the desired temperature,

the current through the diaphragm material The diaphragm material isinserted between the fixed and movable elements of the clamping deviceso as to rest upon the coplanar surfaces of the block 6 and the mountitsexpanded condition.

ing member 4 between the upper and lower surfaces of the heat insulatingmaterials 28 and 13, respectively. As pointed out above, the surface ofthe mounting member 4 adjacent the diaphragm material is insulatedtherefrom to avoid the possibility of a short circuit occurring whencurrent is flowing through said material. The extremities of thediaphragm material are clamped within the jaws of the elongated clips 7.The operator then closes the switch 11. thereby causing current to flowthrough the closed circuit heating the diaphragm and causing it toexpand equally in all directions in a horizontal plane. When theinstrument 12 indicates to the operator that the diaphragm has reachedits desired temperatureand it will do so very quicklyhe opens the switch11 and simultaneously pulls down the handle 15 to bring the mountingrings together so that the diaphragm material is held therebetween in Itwill be understood that the means for operating the movable element ofthe clamping device is illustrative and that it would be possible tohave it operated upon by a hydraulic or pneumatic ram to ensure greaterforce to bring the mounting rings together. The ring 25 forces thediaphragm material into the groove 24 forming therein a peripheralcorrugation which aids in maintaining the material against peripheralcontraction while the fastening bolts 37 are being thrust through thedrillings 21 of mounting member 2, through the diaphragm material 1, andsecured into the aligned tapped drillings 26 of the mounting member 4.It will be appreciated that although the diaphragm material obstructstheready passage of the bolts 37, the diaphragm material is held inexpanded condition between the ridged and grooved rings and,consequently. the bolts may be forced through the diaphragm material toengage with the drillings 26. The heat insulating plates 13 and 28 actalso to retard the loss of heat from the diaphragm material while it isbeing rigidly clamped between the mounting members. After the mountingmembers have been secured together the clips 7 are removed, the lever 15pushed upwardly to lift the member 14 from the assembly and the latteris removed so that the diaphragm material external the mounting may betrimmed OH". The diaphragm unit. as shown in Fig. 5 to a reduced scale,is now ready for use.

' It will be apparent. that this method and means of uniformlytensioning metallic diaphragms may be used in the production ofdiaphragms' of any size and are conducive to maximum production and. touniforn'iity of product. The method is simple, rapid, accurate andrequires a minimum of skill only on the part of the operator.

What is claimed'is:

1. The method of uniformly tensioning a metallic diaphragm whichcomprises passing an electric current therethrough to cause it toincrease in temperature and to expand, and constraining said diaphragmagainst contraction upon the cessation of said current flow and theconsequent cooling of the diaphragm.

2. The method of uniformly tensioning a metallic diaphragm whichcomprises heating the diaphragm material to a predetermined degree bypassing electric current therethrough whereby the peripheral dimensionthereof increases, and constraining said diaphragm in its expanded stateagainst peripheral contraction upon cooling.

3. A method of tensioning a metallic diaphragm which comprises passingaheating current through the diaphragm material to cause it to expand,securing said diaphragm in its expanded condition to a mounting, andpermitting said diaphragm material to cool, while so constraining itagainst contraction, such constraint inducing the desired tension in thediaphragm.

4;. The method of tensioning a metallic diaphragm which comprisespassing a heating current through the diaphragm material to cause it toexpand, securing said diaphragm material so expanded to relatively coldmounting members, and allowing said diaphragm materialto cool to itsoriginal temperature, whereby the constraint exerted by the mountingmembers prevents contraction of said diaphragm material, and causes tension to be induced therein.

5. The method of uniformly tensioning a metallic diaphragm whichcomprises passing a heating current through the diaphragm material toheat it andto cause it to expand,

and clamping said diaphragm material on a peripheral portion torelatively cold mounting members and simultaneously interrupting theflow of the heating current, wherebythe diaphragm material is preventedby said members from assuming its original condition on cooling.

6. The method of uniformly tensioning a metallic diaphragm whichcomprises passing a heating current through the diaphragm material toheat it and to cause it to expand to a predetermined degree, andclamping said diaphragm material on a peripheral portion to relativelycold mounting members and simultaneously interrupting the flow of theheating current, whereby the diaphragm material is prevented by saidmembers from as suming its original condition on cooling.

7. The method of tensioning a metallic diaphragm which comprisesinserting the diaphragm material in an electrical circuit containing asource of electric current, closing said circuit to produce a currentflow therein, whereby said diaphragm is heated to a desired degree andcaused to expand, securing a portion of said diaphragm material tomounting means to constrain 1t agamst contraction on cooling,whilesimultaneously opening the electrical circuit to cause a. cessationin current flow therein and permitting said diaphragm to cool and tohave the desired tension induced therein.

8. A device for tensioning a metallic. diaphragm which comprisesrelatively movable members, each of which supports a diaphragm mountingmember, one of said relatively movable members having a surface ofthermally nonconductive material, means for connecting said diaphragmmaterial in circuit with a source of electric current, a member ofthermally non-conductive material to be placed upon a portion of saiddiaphragm and of sufficient mass to maintain said diaphragm material ina flat plane, means to control the electrical circuit of which thediaphragm is a part to cause a heating current to pass through saiddiaphragm material to heat it and to cause it to expand to apredetermined degree, and means for clamping said relatively movablemembers together to secure the diaphragm material to its mounting, whilein an expanded condition, whereby on cooling it is constrained againstcontraction and is thereby subjected to tension.

9. In a device for tensioning a metallic diaphragm the combination,comprising a A pair of members, one being stationary and the othermovable relative thereto and each providing a support for a diaphragmmounting member, said stationary member also providing a support for thediaphragm material, an electric circuit including a source of current,means for connecting the dia phragm material. to be tensioned in saidcircuit, means for opening and closing the circuit through saiddiaphragm material, and means for bringing said stationary and movablemembers together.

10. .Means for securing a diaphragm to a mounting, which consists of astationary and a movable member, said stationary member providing asupport for a diaphragm mounting member and a diaphragm and said movablemember being provided with a plurality of spaced projecting portions andwith means for supporting a diaphragm mounting member in alignment withthat supported by the stationary member.

11. Means for securing a diaphragm to a mounting, which comprises astationary and a movable member, each capable of supporting a mountingmember, said movable member in its inoperative position being spacedfrom said stationary member and having a plurality of spaced projectingportions at its periphery, the spaces defined. thereby providingpassage-ways for the insertion of fastening means in said mountingmembers.

12. A device for securing a diaphragm to a mounting member whichcomprises a stationary member and a movable member, means to exert aforce on said movable member, said movable member having a plurality ofspaced projecting portions under which a mounting member may besupported, said spaced rojecting portions acting to distribute the orceimpressed on saidmovable member to sai mounting when the stationary andmovab e members are in operative relation.

13. Means for securing a metallic diaphragm in an expanded condition toa mounting, said means comprising a stationary and a movable member,said stationary member being provided with a heat insulating surface anda depressed portion in which a diaphragm mounting member may be placedand said movable member being provided with a plurality of spacedprojecting portions and with means for supporting a diaphragm mountingmember in alignment with and in spaced relation to that supported by thestationary member.

14. In a device for securing a diaphragm to a mounting, a stationarymember providing a support for a diaphragm mounting member, a movablemember in spaced relation to said stationary member and likewiseproviding a support for a diaphragm mountmg mem er, and means forexerting a force on said movable member to bring said mounting memberstogether so as to secure a diaphragm therebetween, said .movable memberhaving recess defining portions, the recesses providing passageways forthe insertion of fastening means in said mounting members.

In witness whereof, I hereunto subscribe my name this 22nd day of April,1930.

EDWIN H. SMYTHE.

